The statements in this section merely provide background information related to the present disclosure and may, or may not constitute prior art.
Belt Alternator Starter (“BAS”) powertrain systems for hybrid vehicles differ from conventional, non-hybrid systems in that the driving force or torque required to turn the accessory drive belt and related accessories is not always generated from the engine crankshaft through a crankshaft pulley. During engine operation, the engine crankshaft provides the driving force or torque for rotating a Motor Generator Unit (“MGU”), or starter generator, generally providing for taut and slack sides of the drive belt on opposites sides of an MGU pulley. During engine starting using the MGU however, the MGU drives the accessory drive belt and related accessories causing the slack side of the belt to switch to the opposite side of the MGU pulley. Accordingly, belt tensioners are generally required in such systems as are idler pulleys that are used to shorten drive belt spans to thereby minimize the potential for drive belt slack and resulting slippage.
During engine driven operation of the MGU and other accessories, the loads that are placed on the drive belt are determined by the power that is required to drive the accessories, including the MGU unit. The accessory drive loads are relatively light and, accordingly, require moderate to low drive belt tensioning to avoid belt slippage. On the other hand, during engine starting using the MGU, the MGU must supply sufficient power to rotate the engine (crankshaft, pistons, camshafts, etc.) as well as the accessories. Engine starts therefore require a significantly higher level of drive belt tensioning to control motion on the slack side of the belt and to ensure that the belt will not slip. Because of engine packaging requirements, it is common to provide separate tensioner and idler arms and pulleys with different pivot locations to attain the necessary drive belt geometry for proper performance and durability. Multiple tensioners, idler arms and pulleys may increase the space required for the accessory drive system which can adversely impact the packaging of the BAS powertrain system in some vehicle architectures.